Two single strands of deoxyribo- ("DNA") or ribo-("RNA") nucleic acid, formed from nucleotides, (including the bases adenine (A), cytosine (C), thymidine (T), guanine (G), uracil (U), or inosine (I)), may hybridize to form a double-stranded structure held together by hydrogen bonds between pairs of complementary bases. Generally, hydrogen bonding occurs between A and T or U, while G or I are hydrogen bonded to C. Along the chain, classical base pairs AT or AU, TA or UA, GC, or CG are present. Additionally, some mismatched base pairs (e.g., AG, GU) may be present.
Bringing together two single strands of nucleic acid containing sufficient contiguous complementary bases, under conditions that promote their hybridization, results in double-stranded nucleic acid. Under appropriate conditions DNA/DNA, RNA/DNA, or RNA/RNA hybrids can form.
A probe is generally a single-stranded oligonucleotide having a nucleotide sequence complementary to some degree to a nucleic acid sequence sought to be detected ("target sequence"). A probe may be labeled with a reporter group such as a radioisotope, a fluorescent or chemiluminescent moiety, or with an enzyme or other ligand that can be used for detection. Kohne, U.S. Pat. No. 4,851,330, and Hogan et al., International Patent Application No. PCT/US87/03009, entitled "Nucleic Acid Probes for Detection and/or Quantitation of Non-Viral Organisms," both references hereby incorporated by reference herein, describe detection of a nucleic acid sequence using nucleic acid hybridization. Hogan et al., supra, also describe methods for determining the presence of a non-viral organism or a group of non-viral organisms in a sample (e.g., sputum, urine, blood, tissue sections, food, soil and water).
Members of the Mycobacterium avium complex have characteristic biochemical properties. These members can be differentiated into more than one species by nucleic acid probes and other types of analysis (Wayne and Sramek, Clin. Microbiol. Rev. 5:1-25, 1992). The complex includes the species Mycobacterium avium and Mycobacterium intracellulare. Recent work indicates that the complex also includes additional members. (Wayne and Sramek, supra, Frothingham and Wilson, J. Bacteriol. 175:2818 (1993)). Probes which detect members of the M. avium complex have been described (Hogan et al., surra; Woodley et al., Diagn. Microbiol. Infec. Dis. 15:657-662 (1992); Lebrun et al., J. Clin. Microbiol. 30:2476-2478 (1992); Cregan et al., J. Infec. Dis. 166:191-194 (1992); Young EPO No. 528 306 A2, application number 92113540.6, "Mycobacterium Primers and Probes," and Liu et al., PCT US92/06821, "Oligonucleotides Complementary to Mycobacterium Nucleic Acids."